Cancers are the commonest cause for death among all of the causes for death, and the therapies therefor are mainly surgical treatment in combination with radiotherapy and chemotherapy. In spite of the developments of new surgical methods and discovery of new anti-cancer agents in recent years, treatment results of cancers are not improved very much at present except for some cancers. In recent years, by virtue of the development in molecular biology and cancer immunology, cancer antigens recognized by cytotoxic T cells reactive with cancers, as well as the genes encoding the cancer antigens, were identified, and expectations for antigen-specific immunotherapies have been raised (see Non-patent Literature 1). In immunotherapy, to reduce side effects, it is necessary that the peptide or protein recognized as the antigen exist hardly in normal cells and exist specifically in cancer cells. In 1991, Boon et al. of Ludwig Institute in Belgium isolated human melanoma antigen MAGE 1 recognized by CD8-positive T cells by a cDNA-expression cloning method using an autologous cancer cell line and cancer-reactive T cells (see Non-patent Literature 2). Thereafter, the SEREX (serological identifications of antigens by recombinant expression cloning) method, wherein tumor antigens recognized by antibodies produced in the living body of a cancer patient in response to the cancer of the patient himself are identified by application of a gene expression cloning method, was reported (Non-patent Literature 3; Patent Literature 1), and various cancer antigens have been isolated (see Non-patent Literatures 4 to 9). Using a part thereof as targets, clinical tests for cancer immunotherapy have started.
On the other hand, as in human, a number of tumors such as mammary gland tumor and squamous cell carcinoma are known in dogs and cats, and they rank high also in the statistics of diseases in dogs and cats. However, at present, no therapeutic, prophylactic or diagnostic agents exist which are effective for cancers in dogs and cats. Most of tumors in dogs and cats are realized by owners only after they advance to grow bigger, and in many cases, it is already too late to visit a hospital to receive surgical excision of the tumor or administration of a human drug (an anticancer preparation or the like), so that those dogs and cats die shortly after the treatment. Under such circumstances, if therapeutic agents, prophylactic agents and diagnostic agents for cancers effective for dogs and cats become available, their uses for canine cancers are expected to be developed.    Patent Literature 1: U.S. Pat. No. 5,698,396 B    Non-patent Literature 1: Tsuyoshi Akiyoshi, Cancer and Chemotherapy, 24, 551-519 (1997)    Non-patent Literature 2: Bruggen P. et al., Science, 254:1643-1647 (1991)    Non-patent Literature 3: Proc. Natl. Acad. Sci. USA, 92:11810-11813 (1995)    Non-patent Literature 4: Int. J. Cancer, 72:965-971 (1997)    Non-patent Literature 5: Cancer Res., 58:1034-1041 (1998)    Non-patent Literature 6: Int. J. Cancer, 29:652-658 (1998)    Non-patent Literature 7: Int. J. Oncol., 14:703-708 (1999)    Non-patent Literature 8: Cancer Res., 56:4766-4772 (1996)    Non-patent Literature 9: Hum. Mol. Genet 6:33-39, 1997    Non-patent Literature 10: Naokazu Inoue, Ryo Yamaguchi and Masahito Ikawa, Protein, Nucleic Acid and Enzyme, Vol. 50, No. 11, 1405-1412    Non-patent Literature 11: J Cell Sci. 115:1825-35    Non-patent Literature 12: Blood. 95:1788-96    Non-patent Literature 13: Mol Endocrinol. 9:243-54 (1995)    Non-patent Literature 14: J Cell Biol. 145: 83-98 (1999)